1. Field of the Invention
The present invention relates to a pattern forming method in the field of semiconductor and a method of manufacturing a semiconductor device.
2. Description of the Related Art
In recent years, with a downsized element and a highly integrated LSI, there has been a request for resolution equal to or smaller than a wavelength an ultraviolet ray. For this reason, exposure process latitudes such as exposure latitude and focus latitude have been insufficient.
Thus, a liquid immersion exposure technique has been proposed as a technique of improving a resolution by using a conventional exposure light source. The liquid immersion exposure technique, as disclosed in Japanese Patent No. 2753930, is provided as a technique for separating an optical element opposed to a surface of substrate of a projection optical system from a projection optical system main body and using the optical element as a flat shaped element having two surfaces parallel to each other; providing means comprising a container that configures a closed space for filling a liquid between the flat shaped element and the substrate opposed thereto; and carrying out exposure while relatively moving the means and an exposure region on the substrate.
In the liquid immersion exposure technique, there has been studied that a protective film is formed on a resist film in order to prevent entry of an immersion liquid into the resist film or elusion from the resist film into the immersion liquid.
A typical example of a protective film to be formed on a resist film before exposure is, for example, a film which is formed by applying fluorine-based process gas on a surface of a resist film as disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2001-319862.
In contrast, as disclosed in Keita Ishizuka et al., New Cover material Development Status for Immersion Lithography, Web publication of International symposium on immersion and 157 nm lithography, a protective film used in immersion exposure is a film formed as a coating film on a resist film, apart from the resist film.
However, the protective film formed by the method of this type cannot achieve the purpose described previously. For example, Daisuke Kawamura et al., Influence of the watermark in immersion lithography process (SPIE2005) discloses that, as shown in FIG. 1, depending on the shape of an immersion liquid 93 that remains on a protective film 92, the immersion liquid as the droplet 93 penetrates the protective film 92 and reaches a resist film, and a water stain (watermark) 94 occurs on an interface between the protective film 92 and the resist film 91. The immersion liquid 93 shown in FIG. 1 shows a water droplet having a diameter of 0.1 mm.
A behavior of a photosensitizing agent or the like eluting from a film into an immersion liquid is studied with respect to the resist film as well. For example, in Karen Petrillo et al., (SPIE2005 5753-9), there is disclosed that, even in the case of forming a resist film including the same solid component, an eluted amount of a photosensitive substance differs depending on the type of a solvent included in a photosensitizing agent solution, as shown in Table 1 (refer to FIG. 2 for a molecular structure of the solvent). In an example of Table 1, the eluted amount increases in the case where ethyl lactate having alcoholic property OH is included.
TABLE 1Contact angleEluted amountSolvent system(°)(ppb)PGMEA + EL + GBL68.573PGMEA + EL6755PGMEA + GBL6525PGMEA + Cycrohexanon6525
The elusion of a photosensitizing agent or a dissolution inhibitor agent from a resist film into an immersion liquid degrades a resist performance. In addition, an optical system of an exposure apparatus is contaminated with the eluted liquid. The contamination of the optical system degrades an image forming property.
A resist film or a protective film is formed by a rotating coating method. In this technique, baking is carried out after forming a coat film in order to remove a solvent.
The baking is carried out in a humidity-controlled atmosphere. The baking may be carried out in an atmosphere containing a dry air, oxygen, or nitrogen, etc., as disclosed in Jpn. Pat. Appln. KOKAI Publication No. 10-335203. Jpn. Pat. Appln. KOKAI Publication No. 10-335203 discloses selecting a gas which is preferable to an atmosphere at the time of baking and a device for supplying the gas. There is also disclosed that atmosphere switching means can be applied to a cool plate or a device for continuously carrying out a plurality of substrate processings.
After the baking, the substrate is cooled. For example, Jpn. Pat. Appln. KOKAI Publication No. 2001-76984 discloses a technique for substituting a current atmosphere with an inert gas or a purified air atmosphere after carrying out a substrate heating process, and then, cooling the substrate, in order to reduce a cooling time and to make uniform in-plane temperature distributions of a substrate to be processed.
Further, Jpn. Pat. Appln. KOKAI Publication No. 2005-19969 discloses a technique for, with respect to a resist pattern after developed, applying a solvent steam which dissolves the developed resist pattern, thereby smoothening a surface of the resist pattern.